2 files changed, 119 insertions, 3 deletions

diff --git a/src/attributes/mod.rs b/src/attributes/mod.rs
index 7f4fb0d..8f50c56 100644
--- a/src/attributes/mod.rs
+++ b/src/attributes/mod.rs
@@ -20,6 +20,7 @@ mod shape;
 mod spline_type;
 mod splines;
 mod style;
+mod viewport;
 
 pub use crate::attributes::arrow_type::ArrowType;
 pub use crate::attributes::cluster_mode::ClusterMode;
@@ -49,6 +50,7 @@ use indexmap::map::IndexMap;
 use std::borrow::Cow;
 use std::collections::HashMap;
 use Cow::Borrowed;
+use crate::attributes::viewport::ViewPort;
 
 /// The text for a graphviz label on a node or edge.
 #[derive(Clone, PartialEq, Eq, Debug)]
@@ -310,6 +312,13 @@ impl<'a> From<Styles> for AttributeText<'a> {
     }
 }
 
+impl<'a> From<ViewPort> for AttributeText<'a> {
+    fn from(viewport: ViewPort) -> Self {
+        AttributeText::quoted(viewport.dot_string())
+    }
+}
+
+
 impl<'a> From<u32> for AttributeText<'a> {
     fn from(v: u32) -> Self {
         AttributeText::attr(v.to_string())
@@ -853,7 +862,6 @@ pub trait GraphAttributes<'a> {
         self
     }
 
-    // TODO: add a ViewPort Struct?
     /// Clipping window on final drawing.
     /// viewport supersedes any size attribute.
     /// The width and height of the viewport specify precisely the final size of the output.
@@ -865,8 +873,8 @@ pub trait GraphAttributes<'a> {
     /// of the graph,
     /// in points, of the center of the viewport, or the name N of a node whose center should used
     /// as the focus.
-    fn viewport(&mut self, viewport: String) -> &mut Self {
-        self.add_attribute("viewport", AttributeText::attr(viewport))
+    fn viewport(&mut self, viewport: ViewPort) -> &mut Self {
+        self.add_attribute("viewport", AttributeText::from(viewport))
     }
 
     /// Add an attribute to the node.
diff --git a/src/attributes/viewport.rs b/src/attributes/viewport.rs
new file mode 100644
index 0000000..f5bfe92
--- /dev/null
+++ b/src/attributes/viewport.rs
@@ -0,0 +1,108 @@
+use crate::attributes::Point;
+use crate::DotString;
+use std::borrow::Cow;
+
+pub struct ViewPort {
+    pub width: f32,
+    pub height: f32,
+    pub zoom: f32,
+    pub focus: Option<FocusType>
+}
+
+impl ViewPort {
+    pub fn new(width: f32, height: f32, zoom: Option<f32>, focus: Option<FocusType>) -> Self {
+        Self {
+            width,
+            height,
+            zoom: zoom.unwrap_or(1 as f32),
+            focus
+        }
+    }
+
+    pub fn new_point(width: f32, height: f32, zoom: Option<f32>, x: f32, y: f32) -> Self {
+        Self {
+            width,
+            height,
+            zoom: zoom.unwrap_or(1 as f32),
+            focus: Some(FocusType::Point(Point::new_2d(x, y)))
+        }
+    }
+
+    pub fn new_node(width: f32, height: f32, zoom: Option<f32>, node: String) -> Self {
+        Self {
+            width,
+            height,
+            zoom: zoom.unwrap_or(1 as f32),
+            focus: Some(FocusType::Node(node))
+        }
+    }
+}
+
+impl<'a> DotString<'a> for ViewPort {
+    fn dot_string(&self) -> Cow<'a, str> {
+        let mut dot_string = String::from("");
+        dot_string.push_str(
+            format!("{:.1},{:.1},{:.1}",
+                    self.width, self.height, self.zoom
+        ).as_str());
+
+        if let Some(focus) = &self.focus {
+            match focus {
+                FocusType::Point(p) => {
+                    dot_string.push_str(format!(",{}", p.dot_string()).as_str());
+                },
+                FocusType::Node(n) => {
+                    dot_string.push_str(format!(",'{}'", n).as_str());
+                },
+            }
+        }
+
+        dot_string.into()
+    }
+}
+
+pub enum FocusType {
+    Point(Point),
+    Node(String)
+}
+
+
+#[cfg(test)]
+mod test {
+    use crate::attributes::{ViewPort};
+    use crate::DotString;
+
+    #[test]
+    fn viewport_dot_string() {
+        assert_eq!(
+            "1.0,2.0,1.0",
+            ViewPort::new(1.0, 2.0, None, None).dot_string()
+        );
+    }
+
+    #[test]
+    fn viewport_zoom_dot_string() {
+        assert_eq!(
+            "1.0,2.0,3.0",
+            ViewPort::new(1.0, 2.0, Some(3.0), None).dot_string()
+        );
+    }
+
+    #[test]
+    fn viewport_point_focus_dot_string() {
+        assert_eq!(
+            "1.0,2.0,3.0,5.0,10.0",
+            ViewPort::new_point(1.0, 2.0, Some(3.0), 5.0, 10.0).dot_string()
+        );
+    }
+
+    #[test]
+    fn viewport_node_focus_dot_string() {
+        assert_eq!(
+            "1.0,2.0,3.0,'2.8 BSD'",
+            ViewPort::new_node(
+                1.0, 2.0, Some(3.0), String::from("2.8 BSD")
+            ).dot_string()
+        );
+    }
+}
\ No newline at end of file